High Optical Stability Research Articles

Composition Optimization of Multifunctional CsPb(Br/I)3 Perovskite Nanocrystals Glasses with High Photoluminescence Quantum Yield

AbstractCurrently, high optical purity, perfect stability, and high photoluminescence quantum yield (PLQY) are very important, being the key to obtain high‐quality luminescent materials. The research of perovskite nanocrystals (NCs) as optical materials is in full swing. Nevertheless, the low PLQY value, especially for the red‐emitting perovskite NCs, is a main obstacle to applications in display. This work reports the optimized components to synthesize CsPb(Br/I)3 NCs glasses whose PLQY achieves a big boost from 15.4% to ≈60% for the first time. Furthermore, the specimens exhibit exceptional tolerance to water and thermal and hence contribute to applicability in high‐performance light‐emitting diode (LED) and 3D printing. By combining CsPb(Br/I)3 NCs glass powder and yttrium aluminum garnet (YAG):Ce phosphor with blue chips, the assembled white LEDs reach a high luminous efficiency at 113.0 lm W−1. The resulting high PLQY is to the benefit of a substantial step toward the practical application of inorganic perovskite materials in the fields of optoelectronic devices and additive manufacturing.

Highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) as an efficient nanoprobe for imaging of microbial cells

Carbon, being a material of the era, has vast usefulness in the synthesis of many novel compounds. One of them is graphene quantum dots (GQDs) have drawn a great deal of attention to the scientific community owing to their low cytotoxicity, higher optical stability, and tremendous photoluminescence (PL) property, which show a new insight in the field of bio-sensing and bio-imaging. Herein, we have demonstrated a facile method to synthesise N-doped GQDs from graphene oxide (GO) using solvothermal treatment with aprotic solvent. GO was synthesised using a modified Hummers’ method. The as-prepared N-GQDs showed stronger green emission with 326 nm wavelength. PL study showed that PL characteristics of as-synthesised N-GQDs are mainly due to the surface π→π* and n→π* transitions of N containing functional groups with skeletal carbons of the graphene oxide sheet. The N-GQDs were also examined for bio-imaging of microbial cells including E. coli and Saccharomyces cescerevisiae yeast. The results (blue and green emissions under a fluorescence microscope) of this study showed biocompatibility and the photostability of N-GQDs for their application in the fields ranging from energy to biomedicine.

Patterned few nanometer-thick silver films with high optical transparency and high electrical conductivity.

Transparent conductive electrodes (TCEs) are experimentally demonstrated using patterned few nanometer-thick silver films on zinc oxide-coated rigid and flexible substrates. The grid lines are completely continuous, but only 8.4 nm thick. This is the thinnest metallic grid we are aware of. Owing to the high transparency of both the grid lines and spacing, our TCE with an opening ratio (OR) as small as 36% achieves an average optical transmittance up to ∼90% in the visible regime, breaking the optical limits of both the unpatterned film counterpart and the thick grid counterpart (whose optical transmittance is determined by the OR). The small OR enables a low sheet resistance of ∼21.5 Ω sq−1. The figure of merit up to ∼17 kΩ−1 is superior to those of the unpatterned film counterpart, our fabricated 180 nm thick ITO, as well as most reported thick metal grid TCEs. Our ultrathin TCE, firmly attached to the substrate, is mechanically more flexible and more stable than the film counterpart and ITO. As a flexible transparent film heater, it achieves comparable or even superior heating performances with previously-reported heaters and performs well in a thermochromic test.

On-off-on nanosensors of carbon quantum dots derived from coal tar pitch for the detection of Cu2+, Fe3+, and L-ascorbic acid

Novel nitrogen-doped carbon quantum dots (N-CQDs) were synthesized by a chemical oxidation method using medium-low temperature coal tar pitch as the raw material. Such quantum dots were developed as a highly sensitive fluorescent “on-off-on” switch sensor for the selective and simultaneous sensing of Cu2+ and Fe3+. The as-prepared N-CQDs, which emit blue light, were characterized by TEM images, FT-IR spectra, Raman spectroscopy, XPS analysis, fluorescence spectra, and UV–vis absorption spectra. The results showed that the N-CQDs exhibit outstanding optical properties and high optical stability within the pH range of 4–10, with a quantum yield of approximately 7%. Additionally, the material performed as an “on-off” sensor which can be dramatically extinguished by Cu2+ and Fe3+. A linear relationship between Cu2+ and Fe3+ ion concentration and fluorescence intensity was observed in the range from 0 to 50 μM. The limits of detection of the fluorescent sensor toward Cu2+ and Fe3+ were 0.16 μM and 0.173 μM, respectively. The Fe3+-quenched N-CQDs were restored after adding L-ascorbic acid, due to the redox reaction between Fe3+ and L-ascorbic acid, which resulted in the detachment of Fe3+ from the surface of the N-CQDs. The linear range for the detection of L-ascorbic acid was 0–28 μM. Therefore, the amount of L-ascorbic acid can be measured by using the sensing system consisting of Fe3+ and N-CQDs. In consequence, N-CQDs are considered an important material for the detection of Cu2+ and Fe3+ in water samples or L-ascorbic acid in drugs.

A novel sensitive aptamer-based nanosensor using rGQDs and MWCNTs for rapid detection of diazinon pesticide

An optical apta-nanosensor was designed and developed based on reduced graphene quantum dots (rGQDs) and multi-walled carbon nanotubes (MWCNTs) and applied for the selective detection of diazinon as one of the most widely used organophosphorus pesticides. Considering the GQDs and rGQDs high fluorescence emission and optical stability, efficient optical transducers could be designed and precise detection methods could be developed based on such transducers. Herein, by using rGQDs, diazinon specific aptamer, and MWCNTs, a simple economical fluorescence method has been introduced to detect and measure diazinon with the detection limit of 0.4 nM (0.1 µg/L) in the range of 4–31 nM, meeting the specifications and standards set by the European Union and World Health Organization. To assess apta-nanosensor performance, the real application of the novel apta-nanosensor was then validated by detecting and quantifying diazinon in real samples, including tap water, urine, river water, and agricultural runoff water. The obtained results revealed that, due to the lack of binding affinity for the diazinon specific aptamer, the emission recoveries were kept intact in the presence of other pesticides and thereby, the designed apta-nanosensor was able to promptly detect diazinon pesticide with high accuracy and selectivity in real samples. Accordingly, the accurate apta-nanosensor developed in this study provides a sensitive, inexpensive, fast, and portable device for selective detection of diazinon over other pesticides in contaminated regions. The introduced innovative method could also be applied for other pesticides, providing a practical on-site detection approach for real samples of multi pesticides.

Improvement of Characteristics of Metal Doped TiO₂ Thin Film and Application to Perovskite Solar Cell.

Over the past three decades, the development of renewable energy technologies has attracted significant attention to overcome both environmental pollution and global warming. Recently, a new type of solar cell based on an organic-inorganic halide perovskite material has been developed. Perovskite solar cells (PSC) were first reported in 2009; their efficiencies increased rapidly from 3.8% to 22%. PSCs have many advantages owing to their use of simple processing technology and stable materials. Perovskite materials have a general formula of ABX, where A is generally methyl ammonium CH₃NH3+ (MA), B is a metal ion, such as Pb or Sn, and × represents a halogen ion. A distinct advantage of lead-based perovskites (i.e., MAPbX₃) is that their band gaps can be easily tuned, from 1.2 to 2.3 eV, by varying their compositions and anions. Titanium dioxide is as often used as an electron transport layer due to its high chemical and optical stability, non-toxicity, low cost, and resistance to corrosion. TiO₂ films can be characterized by the defects in their preparation, such as density fluctuations, pinholes, and cracks; these defects can reduce electrical conductivity and cause recombination. In this study, we have demonstrated that the electrical conductivity of TiO₂ thin films is improved by its doping with Al3+. When applied to a PSC, the doped thin film improves the charge transfer of the solar cell and increases its efficiency. Our results suggest that Al3+ nanoparticles in the TiO₂ layer may contribute to the improvement of the PSC.

Synthesis, Structural and Spectroscopic investigation of Gd2(WO4)3 phosphor

In the present work we synthesis Gd2(WO4)3 phosphor by hydrothermal method. X-ray diffraction results show that the samples are crystallized in monoclinic crystal structure without any impurity phases. Rietveld refinement data confirms the phosphors belong to space group C2/c. FTIR spectra showed the stretching and bending vibration modes. UV-Visible absorption spectroscopy illustrate the optical band gap (Eg) value of prepared sample. SEM micrographs indicate the agglomerated spherical particles. Gd2(WO4)3 phosphor exhibits high optical and structural stability.

Synthesis of Zinc-Doped Lithium Tantalate Charge in the Technology of Novel Crystalline Functional Materials

A procedure was developed for preparing lithium tantalate (LiTaO3) charge homogeneously doped with lithium from high-purity tantalum-containing solutions, based on heat treatment of lithium-, tantalum-, and zinc-containing citrate precursors. The thermolysis products were studied by thermal analysis, X-ray diffraction, and IR absorption spectroscopy. The optimum synthesis conditions and zinc concentration to obtain a single-phase LiTaO3:Zn charge were determined. Comparison with the properties of an isomorphic compound LiNbO3 (LiNbO3:Zn) demonstrated the advantages of the synthesis procedure developed and practically important properties such as high optical stability of LiTaO3:Zn crystals and low coercive field, acquired by lithium tantalate upon doping with zinc. Samples of LiTaO3:Zn charge of various compositions, suitable both for the technology of LiTaO3:Zn crystals and for the preparation of piezoelectric ceramics based on zinc-doped lithium tantalate, were prepared by the developed procedure.

Synthesis of Ag-loaded TiO<sub>2</sub> multiscale structure by coupling underwater laser ablation with hydrothermal treatment

<p indent=0mm>Due to highly rigid demanding for various functional photocatalysts in energy conversion and environmental applications, TiO₂ stands as one of the most widely studied semiconductors and highlighted for heterogeneous photocatalysts. By splitting water in solar energy conversion cells, it also serves as the promising candidate for photoanode material. The distinguished popularity of TiO₂ is attributed to many advantages, such as relatively high quantum efficiency, low cost, biocompatibility, and high optical and chemical stability. In recent years, controlling the structural parameters of TiO₂ is of particular importance which determines the efficiency and physicochemical properties of the resultant photocatalysts. However, two obvious shortcomings restrict the wide applications of TiO₂. On the one hand, the rapid electron-hole recombination results in low quantum yield, which makes it more difficult to efficiently purify sewage in large scale and concentrated pollutants. On the other hand, due to its wide band gap <sc>(~3.2 eV),</sc> TiO₂ can only take effect in the UV region of the solar spectrum (~5% of the solar energy), while the energy absorption in the range of visible light containing about 45% of the solar energy cannot be captured. In order to extend the spectral range of the TiO₂ response, deposition of noble metals, such as Ag, on TiO₂ serves as one of the effective methods to reduce the chance of electron-hole recombination in photocatalytic process by coupling with the versatile properties of photocatalytic and antibactericidal activities. Ag could contribute to the formation of Schottky barriers at Ag/TiO₂ interfacial contact area, resulting in the reduction of electron-hole recombination in the photocatalytic process. Meanwhile, Ag brings in extra absorption bands at visible light spectra due to surface plasmon resonance (SPR) effect. The spectral range of the response of TiO₂ could be further extended to a much longer wavelength. However, it is found that the controllability of deposition of Ag on TiO₂ surface is weak in the process in regular methods, such as photodeposition, chemical reduction, and thermal impregnation, which usually require complicated equipment or toxic nitrogen for modification of TiO₂ with Ag. Hence, it is desired to explore a simple and nontoxic method to fabricate Ag/TiO₂ composite nanoparticles. Laser ablation is considered as a flexible method to synthesize nanoparticles, offering an alternative green route to well-separated nanoparticles. In this study, a simple, direct and flexible method by coupling pulsed laser ablation with hydrothermal treatment was used to obtain multiscale structured Ag/TiO₂ nanocomposites. Underwater laser ablation of metal targets has the characteristics of instantaneous high temperature and high pressure in heat affected zone due to confinement effect in aqueous condition, while the generated plasma quenched rapidly and formed rich nanostructures. Meanwhile, hydrothermal method shows great convenience for regulating the morphology of nanoparticles, smaller crystal thermal stress, smaller macro defects as well as higher uniformity. By optimizing the sequence of hybrid processing and hydrothermal reaction time, sea urchin structures and dendritic structures of TiO₂ were successfully prepared, enhancing the ultraviolet light absorption by scattering effect in the multiscale structures. Ag nanoparticles were further loaded on TiO₂, avoiding the aggregation and obtaining Ag/TiO₂ composite materials with excellent optical properties. Spherical Ag particles around <sc>20 nm</sc> were dispersedly deposited on the burrs of sea urchin structured TiO₂. Meanwhile, the secondary laser processing provides extra activation energy to further regulate TiO₂ morphology, leading to the formation of dendritic structures. Similar Ag nanoparticles were also successfully deposited or embedded on the surface of TiO₂ dendritic structures in the range of <sc>20–60 nm</sc> width. The crystallinity of as-prepared Ag-loaded TiO₂ is significantly improved by combing the rutile phase of TiO₂ with face-centered cubic structured Ag nanoparticles. The peak of TiO₂ light absorption will be red-shifted in the ultraviolet region and loaded Ag nanoparticles broadens the absorption band in the visible region. Wider absorption spectral band was achieved by Ag/TiO₂ composite with excellent optical properties, which can perform more application prospects in photocatalytic degradation of organic pollutants.

Development of a new multi-mode NIR laser system for photodynamic therapy

Photodynamic Therapy (PDT) has been used in various fields especially in cancer treatment. In PDT, designing a light source has vital importance in order to achieve a successful treatment. Among the light sources, Lasers are important candidates for their precise wavelengths to activate the photosensitizers (PS), coherent nature and fiber-coupled usage. In order to achieve perfect PDT treatment, the Laser light sources needs to be embedded withhigh stability current, temperature controllers and closed loop control systems.In this study, a novel Multi-mode PDT Laser system (MPTL) was developed with four different radiation modes. Importantly, Super Pulse Mode (SPM) was implemented for the first time among the PDT Laser systems in the open literature tominimize the thermal damage to the target tissue. The proposed system achieved high optical output stability by precise current and temperature control of the Laser resonator. The MPTL achieved high optical output stability (±1mW) in the range of 0–1500 mW, high wavelength stability (±1nm) at 635 nm,and high temperature stability (±0.2 °C) in all radiation modes. The MPTL system with super pulse mode can be safely used for wide range of PDT clinical applications.

Construction of Carbon Nanotube Sponges to Have High Optical Antireflection and Mechanical Stability.

Antireflective (AR) materials are required to possess high optical antireflection and mechanical stability for their practical applications in optical, opto-electronic, and electron-optical devices. However, the AR materials developed so far can hardly meet these requirements. Here, we report the construction of a highly porous and sponge-like material based on carbon nanotubes (CNTs). This is achieved by continuous winding of a hollow cylindrical CNT assembly and subsequent modification with amorphous carbon (AC). The resultant material is shown to have very low optical reflectance at the visible and infra-red wavelengths over a wide range of incident angles and undergoes little degradation even after long-lasting compressive cycling between 0 and 90% strains or a large change of environmental temperature from -196 to 300 °C. Besides, the AR sponge material can recover fast after bending, stretching, and compression from high elastic strains. Such an excellent combination of broadband and omnidirectional antireflection, mechanical stability, and elastic flexibility results from the strong light absorption by the highly porous CNT structures strengthened by AC deposition on CNT surfaces and junctions, and the new AR material has potential applications in the renewable energy and military fields.

Synthesis of a Novel CQDs‐GO‐Ag2S Composite and Study on the Adsorption of Methylene Blue

AbstractThe present work aims to develop a composite that takes the advantages of carbon quantum dots (CQDs) such as wide absorption band, high optical absorption coefficient and chemical stability as well as the nano‐sized silver sulfide with excellent redox capacity and the strong absorption in the visible range. Such nanocomposites were crafted on a template developed using polyethyleneimine (PEI) modified Graphene oxide (GO). The adsorption properties of methylene blue dyes were tested. With the large specific surface area, the as prepared nanocomposites achieved the removal rate of the blue dye up to 99.0%. The adsorption process was able to be described using the Freundlich isothermal model, wherein, the maximum adsorption capacity was obtained as 348 mg⋅g−1. Thermodynamic analysis indicates the adsorption is entropy driven process with ΔG &lt; 0, ΔH &gt; 0, and ΔS &gt; 0. The present study shows that CQDs‐GO‐Ag2S composites as a promising adsorbent that may be applied to wastewater treatment and waste gas removal.

Yellow emissive nitrogen-doped graphene quantum dots as a label-free fluorescent probe for Fe3+ sensing and bioimaging

Rapid and sensitive fluorescence nanomaterials sensor with satisfactory selectivity has gained numerous importance for detecting multiple metal ions. Graphene quantum dot (GQD) has attracted a great deal of attentions. Herein, yellow emissive GQDs with a high quantum yield of 0.34 were achieved by nitrogen-doping. The as-prepared N-GQDs exhibited excitation-independent behavior and high optical stability. Furthermore, based on the complexation between Fe3+ and N-GQDs, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of Fe3+ ions. The linearity range is 0–80 μM with a detection limit of 63 nM. For this reason, the proposed method was demonstrated to be selective and suitable for Fe3+ analysis in natural water samples. And, N-GQDs with the biosafety have the potentials for intracellular Fe3+ detection.

Role of surface modification on selenium nanoparticles: Enumerating the optical, thermal and structural properties

The well dispersed and homogenous particles of selenium with nanosized dimension (Se-Nps) in aqueous media were prepared in the current study. Three surfactant with variable nature i.e. cationic (CTAB), anionic (SDS) and non-ionic (Brij-58) were employed to fabricate Se-Nps with high optical and chemical stability. The corresponding effect of variations in the concentration of employed surfactant and Se precursor were investigated on the optical properties, homogeneity rate, polydispersity index (PDI) and hydrodynamic radii of Se-Nps. The thermal changes and nature of nanoparticles as a function of different concentration were investigated out by using differential scanning calorimetric (DSC) analysis. The nature of the utilized surfactants over the surface of the nanoparticles has produced significant effect on the agglomeration number of Se-Nps. The microstructural transformations such as changes in crystalline size, lattice strain were calculated as a function of concentration of employed surfactant and Se precursor. The variations in the deformation stress, strain and energy density for Se-Nps were estimated from X-ray diffraction line broadening methods. The modulation and interacting ability of surfactants with Se was evaluated using Fourier transform infrared (FTIR) spectroscopy. The current studies provide the detailed apprehension into the applications of surfactants to fabricate Se-Nps. The work enumerates that by varying the concentration of surfactant and Se precursor, it is feasible for the tuning of optical, structural and thermal properties of Se-Nps.

Synthesis of high-efficient red carbon dots for pH detection

A facile one-step solvothermal route for the preparation of high-efficient red fluorescence carbon dots (RCDs) is developed using 2-aminophenol as carbon source. The as-prepared RCDs indicate excitation-independent emission at 615 nm, high absolute photoluminescence (PL) quantum yield (24%) in ethanol, excellent water solubility, high optical stability and sensitive pH response behavior. The RCDs-based “off-on” reversible probe can be used to detect H+ and OH−. The quenching and recovering effects can be obviously observed by naked eyes due to the combination effect between the target ions and the surface functional groups of RCDs, resulting in breaking or recombination of the quenchers. Moreover, a remarkable fluorescence enhancement behavior with the increase of pH from 4 to 13 can be induced by the RCDs, which can be also used to detect H+ and OH− in urine of cattle and lake water, exhibiting a promising platform of the RCDs for environmental and biological sensing applications.

Red-Emissive Carbon Dots for "Switch-On" Dual Function Sensing Platform Rapid Detection of Ferric Ions and l-Cysteine in Living Cells.

Ferric ions (Fe3+ ions) and l-cysteine (( l-Cys) in the human body have always played an irreplaceable role in biological processes, and overload or deficiency of Fe3+ ions and l-Cys in the biological system leads to various diseases. In this work, N,S-co-doped red-emitting carbon dots (R-CDs) were synthesized by a facile hydrothermal method. Because the doping of N and S gives a unique functional group distribution on the surface of R-CDs, it can be complexed with Fe3+ ions to construct an energy transfer quenching system. However, the presence of l-Cys competitively binds to Fe3+ ions, thus resulting in the photoluminescence recovery of R-CDs. Therefore, a “switch-on” dual function sensing platform has successfully been developed based on R-CDs for rapid identification and quantification of Fe3+ ions and l-Cys. The linear detection range of Fe3+ ions is 0–30 μM (limit of detection (LOD): 0.27 μM) and that of l-Cys is 0–24 μM (LOD: 0.14 μM). The sensor platform was used to detect Fe3+ ions and l-Cys in human serum samples with satisfactory results. Compared with traditional detection methods, this method is more time-saving and efficient and can be completed in 3 min. It is worth mentioning that the R-CDs not only has high optical stability but also has negligible cytotoxicity and has been successfully applied to in vitro/vivo imaging, indicating that R-CDs have excellent tissue penetration and biomarker potential. More interestingly, the switch-on fluorescence behavior for stepwise detection of Fe3+ ions and l-Cys can also be observed in cell imaging, which provides the possibility of visual detection of the probe to be applied in vivo.

A Novel Ratiometric Fluorescent Probe for Mercury (II) ions and Application in Bio-imaging.

Since the accumulation of mercury (II) ions in the environment and ecosystem causes serious problems to environment and disease, the recognition of Hg2+ ions and its bio-imaging is of high importance. In sight of the advantages of fluorescence probes, a new probe (PMH) was facilely synthesized by incorporating phenylimidazole fluorophore and 3-methyl-2- benzothiazolinone hydrazone hydrochloride monohydrate. The PMH probe exhibited a ratiometric response for Hg2+ ions with fluorescence intensity increasing at 520 nm and decreasing at 445 nm simultaneously. The PMH probe interacted with Hg2+ ions in seconds with high optical stability and showed good selectivity over other metal ions. In addition, the probe has excellent biocompatibility and imaging performance in cells and zebrafish.

P‐69: Light Absorbing Dye‐Doped Siloxane Based Optical Filter Film for Image and IR Sensors

As a demand for thin &amp; flexible optical sensors has increased, conventional glass substrates based optical filters needs to be replaced by flexible film based optical filters. In this paper, light absorbing dye‐doped siloxane based optical film filters are introduced for replacing conventional glass based optical filters. Light absorbing dye‐doped siloxane hybrid optical film filters have good light filtering ability in diverse wavelength ranges with high transmittance in desired wavelengths, showing high thermal and optical stability.

Investigation of the Optical Properties of InSb Thin Films Grown on GaAs by Temperature-Dependent Spectroscopic Ellipsometry

InSb thin films were grown on GaAs substrates by metal organic chemical vapor deposition (MOCVD) and investigated by temperature-dependent spectroscopic ellipsometry (TD-SE). The refractive index, extinction coefficient, and dielectric function of the InSb films were extracted. The variation of critical point energies (E1, E1+Δ1, E2, $$ {E}_1^{\hbox{'}} $$ ) related to the excited state transitions of InSb and the second energy derivatives of the dielectric function at different temperatures showed that the InSb thin film had high electrical and optical stability at the evaluated temperatures. TD-SE analysis revealed a temperature range suitable for the use of InSb/GaAs-based devices. Beyond 250°C, InSb was heavily oxidized to form a thin In-O layer, causing a pronounced change in the optical constants. The results indicated that optimized InSb thin films grown on GaAs by MOCVD possess good optical and structural properties.

Mono-, bi- quinolinium branches carbazole as groove binding mode of two-photon excited fluorescent probe interacting with DNA and nucleus imaging

In this paper, new two-photon fluorescent nucleic acid probes, 3-(N-methyl -2- vinyl quinolinium iodide)-9-ethylcarbazole (M2EQC) and 3,6-di-(N-methyl -2- vinyl quinolinium iodide)-9-ethylcarbazole (DM2EQC), have been designed and synthesized. The two compounds are fluorescent DNA probes with long wavelength emission (670 and 650 nm, respectively) irradiated by near-infrared light. The new probes exhibit an obvious improvement in the two-photon absorption action cross-section (222.68 GM and 290.72 GM, respectively). They show the same nuclear localization level as Hoechst 33342 when staining 3T3 cells together. The bioluminescence imaging effect of the compound’s stained cells excited by the 800 nm laser was better than that at 400 nm. The probes also show three-dimensional imaging capability of a single nucleus and lower cytotoxicity, besides the lower fluorescence bleaching effect and higher optical stability than the reported two-photon nucleic acid probe. The fluorescence decay rate was 0.023%/min and 0.020%/min, respectively. The quantum chemical calculation results reveal the reason for spectra changing and we speculate the mechanism of the probes binding with DNA.